Porsche Cayenne Fuel Economy Challenge: Five engines, one huge test

Five Porsche Cayenne SUVs. One simple goal: We find out which one is the most efficient

PHOTO: Nick Tragianis, Postmedia News

Five Porsche Cayennes, five unique powertrains.

PHOTO: Nick Tragianis, Postmedia News

Five Porsche Cayennes, five unique powertrains.

PHOTO: Nick Tragianis, Postmedia News

By David Booth, Postmedia News

Originally published: September 5, 2013

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The concept of performing a real-world fuel economy evaluation of any Porsche — let alone the company’s big, heavy, not-nearly-tree-huggable SUV — would seem a bit of an oxymoron. After all, with more than 1,800 horsepower and $400,000 in MSRPs shared between the five of them, they are neither likely to show off any particular fossil fuel parsimony nor be bought by a clientele who truly cares about minimizing fuel consumption. Porsches are always about performance, often about ostentation and, depending on the owner, maybe even a touch of classism. But fuel consumption? Pshaw! Testing Porsches for fuel economy is a little like warning politicians not to pad their expenses; both can be made to mind their pennies, but somewhere along the way to Saskatoon, there’s a lot of money spent (see Pamela Wallin.)

Nonetheless, there’s some method to our madness, our original motivation for choosing the seemingly inappropriate Cayenne as our fuel economy guinea pig the incredible diversity of its powertrains — in our case, V6 gas, V6 diesel, V6 hybrid variants as well as two V8s, one naturally aspirated and the other turbocharged — and the conclusions we might be able to draw by testing five virtually identical cars powered by five different powerplants.

Some old news, some new

Of course, some of the conclusions were hardly surprising. There’s precious little headline in noting that the 3.0-litre turbodiesel (sourced from the Audi Q7, among others) proved more frugal than the 3.0L Hybrid (and the others, of course) on the highway. That the diesel was able to achieve such stellar fuel economy — just a little behind a diesel-powered 330 BMW, for instance, and significantly better that a 2.0T-powered Audi A6 — despite being big (2,080 kg) and bluff did not fail to impress.

However, it was a huge surprise to find that this same diesel sipped fewer fossil fuels (9.0 L/100 km versus 10.8 for the Hybrid) while scurrying about town. City fuel economy is supposed to be the very raison d’être of the gasoline/electric hybrid and the combination did not show very well here. Indeed, in all our previous tests (in much smaller cars, mind you) the hybrids always proved more frugal than the diesels in urban driving situations.

The difference is in the weight

Why the difference with the Porsches? A partial explanation is that the Cayenne Hybrid is tuned for performance rather than fuel economy. Its stats — 380 horsepower and a time of 6.5 seconds to 100 km/h — read more like a motor head’s dream than that of an enviroweenie. And the Hybrid, thanks in part to its 1.7 kilowatt-hour nickel metal hydride battery, weighs 180 kg more. Nonetheless, the dramatic swing in urban consumption (as we’ve said, never in our previous tests had a diesel beaten a hybrid in the city) makes one wonder if heavier vehicles are better served by diesels rather than by hybrid technology.

This notion is reinforced by the second surprise of the test, namely that the 3.0L diesel Cayenne feels decidedly sportier than its hybrid sibling, despite all the specifications indicating otherwise. Besides those 380 horses (versus just 240 hp for the diesel), the maximum acceleration numbers aren’t even close (6.5 seconds to 100 km/h for the Hybrid versus 7.6 for the turbodiesel). Even the torque figures, usually a strong point for the diesel fraternity, are in favour of the gasoline/electric combination (428 pound-feet for the Hybrid, 406 lb-ft for the diesel). And yet, in all qualitative measures of performance other than full-throttle acceleration, the diesel was significantly superior. Jump off the line was more authoritative, passing on the highway more confidence inspiring and the responsive turbodiesel had a lot less "lag" in its throttle than the comparatively lethargic Hybrid. Indeed, other than the mondo-turbocharged Turbo S, the diesel felt peppier than any of the other Cayennes tested (and, yes, that includes the 400-hp V8 Cayenne S also included in the test).

There are still surprises in store

There was less surprise offered by the other powertrains, though a few interesting points remain. The base 3.6L V6, for instance, achieved 8.9 L/100 km at 120 km/h, just 0.6 removed from the Hybrid. Even the two V8s were not that far behind, at 9.2 L/100 km for the S and 9.3 L/100 km (seriously!) for the Turbo S. A more typical hierarchy was restored while driving in the city, the V6 averaging 11.5 L/100 km, the V8 S 13.0, and the Turbo S 13.9 — the naturally aspirated V8 finally posting more of the expected advantage over the turbocharged sibling. And, as would be expected, the base V6 version felt noticeably lethargic compared with the two V8s (and the diesel).

But, if the driving impressions seemed to highlight the diesel’s advantages, then our perusal of the cars’ respective price sheets cemented its star power. A base V6 Cayenne retails for $57,500 (all pricing for 2014 models) while the diesel is but a pittance more at $65,500. The Hybrid, on the other hand, starts at $80,400, an unconscionable amount considering the diesel’s advantages. Of course, the Turbo S is in another universe, starting at $166,600, though the Cayenne V8 S surprised everyone with its $75,400 sticker.

The numbers are in diesel’s favour

The numbers only get better for the diesel. That $57,500 entry price is for the V6 with the manual transmission. Factor in the same automatic box as the diesel ($60,930) and its price advantage is only $4,570, a small sum compared with the performance and fuel economy advantages the diesel offers.

In the end, the standout was the Cayenne Diesel, which offered the best combination of value, performance and fuel economy — though it must be said that, despite being nonsensical in every quantifiable way, every one of our testers wanted to drive the Turbo S home. Nonetheless, this was a fuel economy evaluation and the clear winner was the vehicle with the compression-ignited Cayenne.

Conclusions

A few (more esoteric) observations before we leave you: Besides the possibility that diesel is more suited to larger vehicles, the other startling difference between this test and others we’ve conducted before was that the Turbo S all but matched its naturally aspirated sibling’s consumption. Previous tests — for the turbocharged Ford Fusion, for instance — showed the turbocharged engines far more profligate.

The difference is easily explained. In the case of Ford’s 2.0L EcoBoost four, even cruising at a relatively sedate 100 and 120 km/h, its turbocharger is already active, reducing any fuel economy advantage it might have had at a slower 60 or 80 km/h. But the hugely powerful Porsche V8 is fairly wafting along, even at 120 km/h its turbocharger completely dormant and, therefore, not sucking back gas.

The last point is that, in every single case in this test, Porsche’s official fuel economy ratings from Natural Resources Canada were remarkably close to the real-world figures observed. In fact, all five Porsches were the closest to their rated consumption than any vehicle we’ve previously tested (in contrast to Ford’s, which are the most exaggerated we’ve observed). Whether it’s superior engineering or simply more rigorous testing, it certainly does lead to more confidence in the product.